This invention relates to liquid check valves and more particularly to an improved check valve for permitting flow of liquid in a first direction and preventing substantial flow in the opposite direction, while also preventing pressure build-up in the liquid on the downstream side of the valve.
In a municipal water supply system, in the event of a failure in the water supply, due for example to a water main break, a siphoning effect may cause water to flow back into the main conduit. Ordinarily, this is not a serious problem. However, if a particular water customer happens to be filling a vessel with water through a hose at the time the break occurs, and the hose is immersed in the liquid in the vessel, the liquid will be drawn through the hose and ultimately into the main conduit. When the break is repaired, the liquid will be present as a contaminant in the water delivered not only to the particular customer, but also to the customer""s neighbors. For example, swimming pool water can be drawn into the main conduit. Worse yet, fertilizers, herbicides pesticides, and other noxious materials can appear as contaminants in a common water supply as a result of siphoning.
To guard against such contamination of the water supply, a check valve is frequently installed in homes and other buildings, usually in the main water line near the water meter, to prevent siphoning of water back into the common supply conduit in the event of a water supply failure. The check valve is typically in the form of a flapper valve built into a brass fitting which is installed in the user""s main water line.
In a municipal water supply system, the pressure of the water delivered to the utility""s customers ordinarily corresponds to the regulator setting at the utility""s pumping facility, or to the height of the water in a tower or standpipe used as a local reservoir. Thus, in the absence of a check valve, the water pressure in a customer""s water lines will not ordinarily exceed the supply pressure. However, when a check valve is installed in the water supply line to a house, for example, the pressure in the water lines throughout the house is no longer necessarily regulated by the supply pressure. Thus, the water heater may cause the pressure to rise excessively, to be relieved only when someone opens a faucet.
Repeated application of excessive pressure to the interior of a water heater is known to accelerate heater failure. Moreover, if the safety relief valve, which is required on all water heaters, fails to release water during an overpressure condition, breakage of the water heater or of a pipe or fitting can occur.
The principal object of this invention is to provide a liquid check valve which not only avoids the undesirable effects of reverse flow when the pressure on the upstream side of the check valve falls rapidly, but which also prevents gradual build-up of pressure on the downstream side of the check valve by allowing for pressure equalization.
In general, a pressure equalizing check valve in accordance with the invention comprises a liquid conduit having an inlet port and an outlet port, the liquid conduit being closed except for the inlet and outlet ports. A valve seat and cooperating main valve closure element are provided within the liquid conduit. The main valve closure element is movable, in response to flow of liquid in a first direction through the conduit from the inlet port toward the outlet port, to an open position in which it is out of contact with the seat and permits free flow of liquid through the conduit, and in response to flow of liquid in a second direction opposite to the first direction through the conduit from the outlet port toward the inlet port, to a closed position in which it is in contact with the seat, and at least substantially retards flow through the conduit in the second direction. A restricted passage connects the inlet port to the outlet port at least when the main valve closure element is in its closed position. An auxiliary valve controls flow through the restricted passage when the main valve closure element is in its closed position. The auxiliary valve comprises an auxiliary valve closure element and an auxiliary seat. The auxiliary valve closure element is normally held away from the auxiliary seat and engageable with the auxiliary seat in response to flow of liquid through the restricted passage, from the outlet port toward the inlet port, at a rate in excess of a predetermined rate, to shut off flow of liquid through the auxiliary passage substantially completely. Thus, when the main valve closure element is in its closed position, the auxiliary valve permits slow flow of liquid through the restricted passage in the main valve closure element so that the liquid pressure at the outlet port is held at a level substantially equal to the liquid pressure at the inlet port. However, when the liquid pressure at the inlet port drops substantially below the liquid pressure at the outlet port, the auxiliary valve closes, thereby substantially completely shutting off flow through the conduit in the second direction.
A pressure equalizing check valve in accordance with a preferred embodiment of the invention utilizes a pivoted flapper as the main valve closure element, as in a conventional check valve. However, the check valve includes an auxiliary valve incorporating a moving ball. The auxiliary valve is normally open, preventing the pressure on the downstream side of the check valve from significantly exceeding the pressure on the upstream side. Thus, even when the check valve is closed, as a result of absence of demand, the pressure on the downstream side will follow variations in upstream pressure and will correspond closely to the pressure on the upstream side. However, when a relatively sudden decrease in upstream pressure is experienced, the auxiliary valve will close, preventing siphoning of liquid from the downstream side to the upstream side.
The auxiliary valve is preferably built into, and carried by the flapper, keeping the device structurally simple and compact, and also making it possible, in some embodiments, to remove the auxiliary valve assembly for repair or replacement by simply removing the flapper and auxiliary valve assembly as a unit, leaving the check valve body in place on the line in which it was installed.
The ball can be heavier than water, in which case, the seat engaged by the ball should face downward when the flap is closed. Alternatively, the ball can be lighter than water, in which case the seat should face upward when the flap is closed.